AstraZeneca believes the technology could help to open up a market where the vaccination rates are only 35 per cent among the elderly and those with chronic heart and lung diseases — those most at risk from flu-linked deaths.

It also thinks the spray will prove popular with countries vaccinating schoolchildren who might be afraid of needles.

The spray is a niche product in the U.S. compared with injected vaccines but demand is increasing. MedImmune said last year it was planning to triple production to 12 million doses for the 2009 flu season.

At the moment, six European countries — Finland, Austria, Estonia, Latvia, Slovakia and Slovenia — recommend vaccinating young children but AstraZeneca will look to sell the spray across the continent. The company’s shares rose 93p to 2792p.